Method for communicating in a network and radio stations associated

ABSTRACT

The present invention relates to a method for communicating in a network comprising a primary station and at least one secondary station, said secondary station comprising a buffer containing data packets to be transmitted to the primary station, the method comprising the step of the secondary station transmitting an indication of the buffer status to the primary station, said indication comprising information about history of said buffer.

FIELD OF THE INVENTION

The present invention relates to a method for communicating in a networkand to radio stations carrying out this method. More specifically, thisinvention may be implemented in a mobile communication network, like aUMTS system.

BACKGROUND OF THE INVENTION

Many communication systems operate using a centralised scheduler whichis responsible for allocating transmission resources to different nodes.A typical example is the uplink of the UMTS LTE (Long Term Evolution),where the uplink transmissions from different secondary stations ormobile station or User Equipments (UEs) are scheduled in time andfrequency by the primary station or base station or Node B (eNB). Theprimary station transmits a “scheduling grant” message to a secondarystation, indicating a particular time-frequency resource for thesecondary station's transmission typically around 3 ms after thetransmission of the grant message. The grant message also typicallyspecifies the data rate and/or power to be used for the secondarystation's transmission.

In order for the primary station to issue appropriate grants, it needsto have sufficient information about the amount, type of data and theurgency of it awaiting transmission in the buffer of each secondarystation. This information can be used to inform the scheduler in theprimary station of either the satisfaction level of individual secondarystations or secondary stations whose service might be close to beingdropped.

In LTE, a number of different types of buffer status report (BSR)messages are therefore defined, which may be transmitted from asecondary station to the primary station when certain triggers occur.The state of the art in this respect is defined by the current versionof 3GPP TS36.321 (as of June 2008), §5.4.5, incorporated herein byreference.

The Buffer Status reporting procedure is used to provide the servingprimary station with information about the amount of data in the Uplinkbuffers of the secondary station. This is currently defined in 36.321(as of June 2008), §6.1.3.1 incorporated herein by reference. A problemwith this procedure defined in 36.321 is that the content of the bufferstatus report only identifies the total amount of data in bytes. Thisgives some information to scheduler but this may not be sufficient forthe scheduler in the primary station to make the best possible decision,especially in some situations, as for example when VoIP traffic is beingtransmitted perhaps together with other services from the secondarystation with different Quality of Service (QoS) requirements, whereabsolute data buffer size in bytes is not the most appropriate measureof how the QoS requirement is currently being satisfied.

SUMMARY OF THE INVENTION

It is an object of the invention to propose a method for communicatingalleviating this problem.

Another object of this invention is to provide a method forcommunicating in a network which provides with appropriate informationto the primary station.

Still another object of the invention is to provide a method forcommunicating in a network which enables to gives the primary stationsufficient information without causing too much overhead.

In accordance with a first aspect of the invention, a method is proposedfor communicating in a network comprising a primary station and at leastone secondary station, said secondary station comprising a buffercontaining data packets to be transmitted to the primary station, themethod comprising the step of the secondary station transmitting anindication of the buffer status to the primary station, said indicationcomprising information about at least one of history and future of saidbuffer.

In accordance with another aspect of the invention, a secondary stationis proposed, said secondary station comprising a buffer containing datapackets to be transmitted to a primary station, the secondary stationcomprising transmitting means for transmitting an indication of thebuffer status to the primary station, said indication comprisinginformation about history of said buffer.

These aspects of the invention are based on the recognition thatadditional information could be incorporated in Buffer Status Report.Indeed, it would be preferable for the secondary station to indicateother indicators of the buffer as an alternative to or in addition tothe total size.

Such indicators could include:

-   -   An indication of the age of the oldest packet in the buffer    -   An indication of the number of packets dropped by the secondary        station due to a delay constraint being exceeded.    -   Number (or total size of) re-transmissions.    -   Prediction of future transmissions. As a consequence, a primary        station will benefit from additional information other than the        amount of data in the buffer in order to make the best decision        on the uplink resources to grant the secondary station. If the        secondary station is able to also inform the primary station of        the age of the packets in the data buffer and/or any dropped        packets and/or the number of packets under retransmission, then        the scheduler performance and overall system performance in        terms of spectrum efficiency will be improved. For example the        performance of a proportionate fair scheduling algorithm in the        primary station can be improved with improved information on the        Quality of Service of the services being transmitted by the        secondary station.

These and other aspects of the invention will be apparent from and willbe elucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in more detail, by way ofexample, with reference to the accompanying drawing, wherein:

FIG. 1 is a block diagram of a network in which the invention isimplemented.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a system of communication 300 asdepicted on FIG. 1, comprising a primary station 100, like a basestation, and at least one secondary station 200 like a mobile station.

The radio system 300 may comprise a plurality of the primary stations100 and/or a plurality of secondary stations 200. The primary station100 comprises a transmitter means 110 and a receiving means 120. Anoutput of the transmitter means 110 and an input of the receiving means120 are coupled to an antenna 130 by a coupling means 140, which may befor example a circulator or a changeover switch. Coupled to thetransmitter means 110 and receiving means 120 is a control means 150,which may be for example a processor. The secondary station 200comprises a transmitter means 210 and a receiving means 220. An outputof the transmitter means 210 and an input of the receiving means 220 arecoupled to an antenna 230 by a coupling means 240, which may be forexample a circulator or a changeover switch. Coupled to the transmittermeans 210 and receiving means 220 is a control means 250, which may befor example a processor. Transmission from the primary radio station 100to the secondary station 200 takes place on a downlink channel 160 andtransmission from the secondary radio station 200 to the first radiostation 100 takes place on an uplink channel 260.

From time to time, the secondary station 200 transmits on the uplinkchannel 260 an indication of the status of its buffer containing data tobe transmitted. This Buffer Status Report can be of different types. Ashort Buffer Status Report (BSR) comprises the identity of a singlegroup of logical channels, together with a 6-bit indicator of the amountof data corresponding to that group of logical channels currentlyresiding in the secondary station's buffer awaiting transmission. A longBSR comprises 4 concatenated short BSRs, each corresponding to adifferent group of logical channels.

The present invention provides a means to send a buffer status reportfrom the secondary station 200 including in a first embodiment at leastone indication of one of the following indicators of the buffer as analternative to or in addition to the total size:

-   -   Age of the oldest packet in the buffer like:        -   Age of the oldest packet in the buffer for a specific group            of logical channels defined to have similar QoS requirements        -   Age of the oldest packet across the whole range of logical            channels        -   Age of the oldest packet where the age has passed a            pre-determined threshold    -   Number of packets dropped by the secondary station:        -   Number of packets dropped by the application            -   Possibly reported per logical channel or group of                logical channels        -   Number of packets dropped by PDCP (PDCP SDUs)            -   Possibly reported per logical channel or group of                logical channels    -   Number of packets under re-transmission        -   Possibly reported per logical channel or group of logical            channels        -   Possibly when number of packets buffered exceeds a threshold    -   Number of HARQ (Hybrid Automatic ReQuest) failures.    -   Prediction of future amount of data or transmission rate.

Typically, the age of a packet could be defined in terms of the time atwhich the data was created by an application, or in terms of the timeremaining until it should be delivered to the end destination. Packetsmay be dropped if their age exceeds a threshold (e.g. packets which havebeen in the buffer so long, that they cannot be delivered to the enddestination in time to be useful, or to meet latency requirements).

It is to be noted that the number of packets dropped by higher layers(PDCP) is known only for higher layers, as defined in 36.323, §5.9incorporated herein by reference. It is indicated in that, when theDiscard_Timer expires for a PDCP SDU the secondary station shall discardthe PDCP PDU along with the corresponding PDCP SDU. If the correspondingPDCP PDU has already been submitted to lower layers the discard isindicated to lower layers.

In order that the buffer status report comprise the at least oneindication of at least one of the above indicators, the buffer statusreport may be modified from a buffer status report comprising the totalsize. In accordance with the first embodiment, some mechanisms can beused to indicate that a buffer status report is a modified buffer statusreport, i.e. that something other than size of data in buffer isreported. In accordance with a first example of the first embodiment, aSemi-static configuration is proposed by Radio Resource Controlsignalling that certain logical channel groups are reported in terms ofthe modified status instead of buffer data size in bytes. This meansthat parallel signaling or higher layer signalling indicates which typeof indication is comprised in each BSR corresponding to each logicalchannel.

According to a second example of the first embodiment, a buffer statusreport may be either a non-modified buffer status report or a modifiedbuffer status report comprising one or more different types ofindication. Then, the type of BSR is signalled by, for example, one ofthe following:

-   -   one or more bits otherwise used for a logical channel        identification;    -   one value of logical channel ID;    -   one or more bits out of the 6 bits allowed for the buffer status        report.        In the latter of these examples, a reduced number of bits        reported in the BSR can be used for the buffer status reporting.        For example in some situations not all of the available bits        defined for buffer status reports may be required and        transmitted, for example when lower bit rate services such as        VOIP are being transmitted. The remaining bits could be used to        indicate which kind of indication is used. This modified number        of bits for the value of the buffer status report could be for        example dependent on system bandwidth and/or UE capability        class.

For example, in small bandwidth cells where a large range of values isnot required to report the smaller maximum amount of data that can besent in one transport block in a TTI, some bits in the BSR can be usedto indicate the kind of indication used, or to indicate the value of asecond kind of indication.

As another example, a UE of a low capability class would not need to beable to report the full range of values which can be signalled with 6bits, and therefore some bits in the BSR can be used to indicate thekind of indication used, or to indicate the value of a second kind ofindication.

In the above two examples, the signalling to indicate the modificationof the BSR is implicit in the signalling of the system bandwidth or UEcapability class respectively.

According to another example of the first embodiment, the type ofindication comprised in a buffer status report may be semi-staticallyconfigured by RRC (Radio Resource Control) signalling. This RRCsignalling may apply to one, more than one or all logical channels orlogical channel groups. Thus a parameter such as a logical channelidentity may be configured to correspond to a particular indicator fromthe above list.

According to another example of the first embodiment, the type ofindication comprised in a buffer status report may be indicated bypre-configuring specific combinations of buffer reports to correspond toan indicator from the above indicators.

It should be understood that the preceding examples could be usedwhatever the indicated value in the BSR is, and should not limited toindication of history or future of the buffer status.

A modified buffer status report can be sent from time to time instead ofa conventional BSR, and/or in response to some events as explainedbelow.

In some embodiments the criteria used to determine in the primarystation or the secondary station whether a modified buffer status reportis transmitted may depend on at least one characteristic of the data.For instance, depending on:

-   -   An indication of the priority of the data;    -   QoS parameters of the data (e.g. latency requirements, or a        function thereof)    -   an identity of a logical channel or group of logical channels to        which the data is assigned;    -   the amount of data which had arrived in the buffer;    -   the rate of arrival of data in the buffer;    -   the time since the previous arrival of data in the buffer.

In accordance with the UMTS specification, a Buffer Status Report (BSR)shall be triggered if any of the following events occur:

-   -   Uplink data arrives in the secondary station transmission buffer        and the data belongs to a logical channel with higher priority        than those for which data already existed in the secondary        station transmission buffer, in which case the BSR is referred        below to as “Regular BSR”;    -   Uplink resources are allocated and number of padding bits is        larger than the size of the Buffer Status Report MAC control        element, in which case the BSR is referred below to as “Padding        BSR”;    -   a serving cell change occurs, in which case the BSR is referred        below to as “Regular BSR”;    -   the PERIODIC BSR TIMER expires, in which case the BSR is        referred below to as “Periodic BSR”.

For Regular and Periodic BSR:

-   -   if only one Group of logical channels (LCG) has buffered data in        the TTI where the BSR is transmitted: report short BSR;    -   else if more than one LCG has buffered data in the TTI where the        BSR is transmitted: report long BSR.

For padding BSR:

-   -   if the number of padding bits is equal to or larger than the        size of the Short BSR but smaller than the size of the Long BSR,        report Short BSR of the LCG with the highest priority logical        channel with buffered data;    -   else if the number of padding bits is equal to or larger than        the size of the Long BSR, report Long BSR.

If the Buffer Status reporting procedure determines that a BSR has beentriggered since the last transmission of a BSR:

-   -   if the UE has UL resources allocated for new transmission for        this TTI:    -   instruct the Multiplexing and Assembly procedure to generate a        BSR MAC control element;    -   restart the PERIODIC BSR TIMER.    -   else if a Regular BSR has been triggered since the last        transmission of a BSR:    -   a Scheduling Request shall be triggered.

Even if multiple events occur by the time a BSR can be transmitted, onlyone BSR will be included in the MAC PDU. A pending BSR shall becancelled in case the Uplink grant can accommodate all pending data butis not sufficient to accommodate the BSR MAC control element inaddition. Similarly, these events may cause the triggering of a modifiedBSR.

Note also that an embodiment in which the secondary station configures apattern in time is possible for the transmission of modified bufferstatus reports which contain alternative secondary station bufferinformation.

In accordance with the first embodiment, the method could comprise aconfiguration in which the primary station configures every Xth bufferstatus reports to indicate number of dropped packets in the periodcorresponding to the last X previously reported buffer status reports.

A further example of this embodiment could comprise a configuration inwhich the primary station configures that any buffer status reports inevery Yth radio frame shall indicate the number of dropped packets inthe period corresponding to predetermined number of previously reportedbuffer status reports.

This invention may be implemented in mobile communication systems wherecommunication devices utilize centralized scheduling, such as UMTS andLTE.

Moreover, this invention could as well be implemented for hubs whichroute calls from multiple terminals to base stations. Such devices wouldappear like a secondary station from the point of view of the network.

In the present specification and claims the word “a” or “an” precedingan element does not exclude the presence of a plurality of suchelements. Further, the word “comprising” does not exclude the presenceof other elements or steps than those listed.

The inclusion of reference signs in parentheses in the claims isintended to aid understanding and is not intended to be limiting.

From reading the present disclosure, other modifications will beapparent to persons skilled in the art. Such modifications may involveother features which are already known in the art of radio communicationand the art of transmitter power control and which may be used insteadof or in addition to features already described herein.

1. A method for communicating in a network comprising a primary stationand at least one secondary station, said secondary station comprising abuffer containing data packets to be transmitted to the primary station,the method comprising the step of the secondary station transmitting anindication of the buffer status to the primary station, said indicationcomprising information about at least one of history and future of saidbuffer.
 2. The method of claim 1, wherein the information about historyof said buffer comprises an indication of the age of the oldest datapacket currently stored in the buffer.
 3. The method of claim 1, whereinthe information about history of said buffer comprises an indication ofthe age of the oldest data packet for a set of logical channels havingsimilar quality of service requirements, and currently stored in thebuffer.
 4. The method of claim 2, wherein the indication of the age ofthe oldest data packet is an indication of whether said age is above apredetermined threshold.
 5. The method of claim 1, wherein theinformation about history of said buffer comprises an indication of thenumber of data packets dropped by the secondary station.
 6. The methodof claim 1, wherein the information about history of said buffercomprises an indication of the number of data packets being currentlyunder retransmission.
 7. The method of claim 5, wherein the number ofdata packets dropped is estimated for groups of logical channels.
 8. Themethod of claim 1, wherein the step of the secondary stationtransmitting an indication of the buffer history is carried out if oneof the following conditions is fulfilled: a priority of any of the datapackets in the buffer is above a predetermined threshold, the rate ofarrival of data in the buffer is above a predetermined threshold, thenumber of data packets in the buffer is above a predetermined threshold,the number of data packets arrived in the buffer is above apredetermined threshold, the amount of data in the buffer is above apredetermined threshold.
 9. The method of claim 1, comprising the stepof the secondary station transmitting an indication of the buffer statuswithout information about history of the buffer at regular intervals,wherein the step of transmitting the indication with information onhistory of the buffer is carried out if one of the following conditionsis fulfilled: a priority of any of the data packets in the buffer isabove a predetermined threshold, the rate of arrival of data in thebuffer is above a predetermined threshold, the number of data packets inthe buffer is above a predetermined threshold, the number of datapackets arrived in the buffer is above a predetermined threshold, theamount of data in the buffer is above a predetermined threshold.
 10. Asecondary station (200) comprising means for communicating with aprimary station (100), said secondary station comprising a buffercontaining data packets to be transmitted to the primary station, thesecondary station comprising transmitting means (210) for transmittingan indication of the buffer status to the primary station, saidindication comprising information about history of said buffer.
 11. Aprimary station (100) comprising means for communicating with at leastone secondary station (200), said primary station comprising means forreceiving an indication of the buffer status from the secondary station,said indication comprising information about history of said buffer, andallocation means for allocating a transmission resource to the secondarystation in accordance with the information about history of the buffer.